Coated piezoelectric analyzers

ABSTRACT

Piezoelectric and magnetostrictive materials coated with charge transfer complexes of halogens are effective detectors for materials capable of being halogenated, such as olefins.

O Umted States Patent 91 [111 3,744,296 Beltzer July 10, 1973 1 COATEDPIEZOELECTRIC ANALYZERS [56] References Cited [75] Inventor: MortonBeltzer, Westfield, NJ. UNITED STATES PATENTS z 3,194,053 7/1965 Shang73/23 [73] Asslgnee gz g ifi i g g g f 3,260,104 7/1966 King, Jr. 73 233,329,004 7/1967 King, Jr. 73/23 [22] Filed: May 7, 1971 [21] AppL NOJ141,335 Primary Examiner-Joseph Scovronek Attorney-Manahan & Wohlers andJoseph J. Dvorak [52] U.S. Cl. 73/23, 23/230 M, 23/232 E,

23/253 TP, 23/254 E, 338/13 [571 ABSTRACT 3 G011! G011 29/22Piezoelectric and magnetostrictive materials coated [58] Field of Search23/232 R, 232 E, with charge transfer complexes of halogens are efiec-23/254 R, 254 E, 255 R, 255 E, 253 TP, 253 R, 230'l-lC, 230 M; 73/23,26, 27; 338/13; 310/8, 8.9

tive detectors for materials capable of being halogenated, such asolefins.

l3 Claims, 1 Drawing Figure PAIENIED JUL 1 0191;

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EZQELECTRIC CRYSTAL W A SUBSTRATE I. R R ECO DE MERCURY csu. J

Marlon Bel/zer INVENTOR BY'W/ COATED PIEZOELECTRIC ANALYZERS BACKGROUNDOF THE INVENTION Coated piezoelectric analyzers have gained considerablecommercial acceptance in numerous scientific and industrialapplications. For example, in gas chromatography, it is necessary todetermine the composition of gaseous effluent. Coated piezoelectriccrystal analyzers are particularly useful in such applications,especially where the concentration of the gas to the detector isextremely low. In addition, many simple analyzers have been developedfor determining moisture or water content in fuels and in otherfluid-feed materials. Other areas of application include the analysisofhydrogen sulfide, aromatics, olefins, and paraffins. These uses, ofcourse, are of particular interest in the petroleum industry.

The fundamental principle of a detection device using a coatedpiezoelectric crystal is set forth in U.S. Pat. No. 3,164,004 which isincorporated herein by reference. Consequently, only so much of thereferenced patent will be repeated as is considered necessary tounderstand the present invention.

Very briefly, piezoelectric and magnetostrictive materials when coatedwith a substrate selectively sensitive to changes in their environmentcan serve as detection devices for use in analyzers. Thus, when aresponsive material which is coated with a substrate is placed in asuitable oscillation circuit, it will vibrate at a particular naturalfrequency. The changes in the environment to which the substrate issensitive will result in changes in the vibrational frequency of theresponsive material.

By the term substrate generally is understood to mean any thin film orcoating deposited in a predetermined quantity on a responsive material.The substrate may be either liquid or solid.

Responsive material is, of course, any material which exhibitspiezoelectric or magnetostrictive properties.

Very briefly, the operability of such detection devices depends upon theinteraction of the substrate with the material to be detected.Interaction is generally understood to mean any physical or chemicalrelationship between the coating and the material which will tend toincrease the resistance of the crystal to the electrical driving forceof the oscillating circuit. As will be more fully explained, interactionalso may include a physical or chemical relationship between the coatingand the material detected which will decrease the resistance of thecrystal. Suffice it to say that generally interaction is thought of interms of weight gain. The greater the weight gain, the less thefrequency of the crystal. Illustrative of interactions are adsorption,absorption, chem-adsorption, chemical reactions, and the like.

Ideally, a coated crystal detector should not only be reusable but thefrequency of the responsive material should return to a natural stablecondition after purging the coating material subsequent to interaction.

Also, substrates employed in crystal detectors are apaccuracy that canbe used and reused in the analysis of fluid materials.

The present invention is concerned with such piezoelectric crystaldetectors. More specifically, the present invention is concerned with amethod and apparatus for detecting materials capable of beinghalogenated.

SUMMARY OF THE INVENTION According to the present invention, apiezoelectric element for fluid detectors is provided which comprises aresponsive material coated with a halogen complex of a charge transfermaterial.

One embodiment of the inventive piezoelectric detector element comprisesa quartz crystal provided with a halogen complex of a charge transfermaterial. Preferably the charge transfer material is a polymeric material that has an endocyclic nitrogen atom in the repeating unit of thepolymer.

In another embodiment of the present invention, a method is provided fordetecting materials capable of being halogenated. Fluid materialssensitive to being halogenated are exposed or contacted with the coatedpiezoelectric detector of the present invention. Upon contact with thecrystal, the fluid material is halogenated resulting in a weight changein the substrate. Thus, the responsive material will exhibit a change inits frequency of oscillation. By detecting this weight change,correlation can be established for analytical and detection purposes.

BRIEF DESCRIPTION OF DRAWING The figure is a schematic diagram of atypical oscillator circuit having a detector element of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION The particular responsivematerial" which may be employed in accordance with this invention isdefined as any material which exhibits piezoelectric or magnetostrictiveproperties.

Material which exhibits piezoelectric properties is one which whensubject to mechanical pressure develops an electric potential, and viceversa, when subject to an electric potential, mechanically deforms.Several such materials are known, for example, crystal such as quartz,tourmaline, and Rochelle salts and other materials such as bariumtitanate. Quartz is the particular crystal most often employed inelectrical applications; it is the preferred in the instant inventionalthough it is not limited thereto.

A magnetostrictive material is a material which will produce a magneticfield upon mechanical deformation, and vice versa, which willmechanically deform in the presence of a magnetic field. Examples ofsuch types of magnetostrictive materials are nickel and nickel alloys.

A detecor of the present invention comprises a responsive materialcoated with a halogen complex of a charge transfer material. Chargetransfer materials are generally well known in the art. Typically theyconsist of compounds that may act as electron donors. Thus, a chargetransfer complex is an intermolecular addition compound consisting of anelectron donor molecule and an electron acceptor molecule. The bindingenergy of such materials is due mainly to the dispersion type forcessuch as dipole-dipole forces, accompanied by partial charge. transfer.It is generally understood that electron transfer in such complexesoccurs from donor to acceptor without appreciable energy loss since norearrangement of molecular structure is involved.

Various polymeric materials are known as charge transfer materials.Often these polymeric materials contain a nitrogen atom in the repeatingunit of the polymer which forms a charge transfer complex with halogens.More often still, the repeating unit contains an endocyclic nitrogenatom in a ring having conjugated unsaturation. Typical polymers that areknown to form charge transfer materials are poly (4- vinylpyridine),poly (2-vinylpyridine), poly (2-vinyl quinoline), poly(N-vinylcarbazole), poly (2- vinylpyrimidine), poly (6-vinylpurine), andpoly (2- vinylpyrazine). 1

The halogen complexes of the above charge transfer materials are thespecific substrate of the instant invention. By the term halogen ismeant bromine, chlorine, and iodine as well as the correspondinginterhalogen compounds BrCl, IBr, 1G1, and the like.

One aspect of the present invention is the recognition that such halogencharge transfer complexes can be utilized as a substrate for coatedcrystal detectors. Coatings or substrates of such charge transfercomplexes are not sensitive to moisture and retain the complex halogenrather tenaciously. At the same time the properties of the complexhalogen do not differ from that of free halogen substantially. Thus,halogen complexes of charge transfer materials undergo essentially thesame reactions as uncomplexed halogens. Thus, a material which iscapable of being halogenated can be readily detected by a responsivematerial containing a coating of this invention. For example, olefinsrepresent a class of compounds that are readily halogenated and to whichthe substrate of the instant invention is particularly sensitive.

The amount of substrate that is employed is a significant variable inthe invention. Its volume in relation to the volume of the crystal andits weight are of particular importance in determining the response ofthe detector.

The amount of substrate generally used covers the range of from about 1to about 100 micrograms per square centimeter of responsive material.Larger amounts can be used but difficulty is then encountered inmaintaining the responsive material in a condition of stableoscillation. Therefore, the amount often is chosen experimentally forthe best compromise.

As stated previously, quartz is the particular crystal most oftenemployed in electrical applications and is the preferred crystalemployed in the present invention. Generally, the crystal has a diameterof about 1.2 centimeters and a thickness of about 0.16 centimeters.

it is preferred in the present invention that the coating of substratebe located essentially uniformly in the region or vicinity of maximumoscillation in the responsive material. The particular area of maximumoscillation of the responsive material will be apparent to one skilledin the art. A responsive material of the dimensions previously mentionedand having electrodes that contact opposite faces of the crystal wouldhave a substrate located over one of the electrodes. The substrate, ofcourse, could extend beyond the borders of the electrode and indeed itcould cover the entire responsive material. Covering the entireresponsive material, however, can be wasteful of substrate and it is notnecessary.

There are various techniques for applying the substrate of the instantinvention on the crystal. For example, the halogen complex of the chargetransfer material can be dissolved in a suitable solvent and painted onthe crystal. After applying the solution to the crystal, the solvent canbe evaporated. Similarly, suspensions of the substrate can be employed.

Solvents particularly useful in dissolving transfer materials of thetype herein specified include the following: propylene carbonate,dimethylsulfoxide and dimethyl formamide. Useful liquids for suspendingsubstrate material include the following: benzene, toluene and water.

The crystal type that is described above can be eniployed in a typicaloscillator circuit such as that shown in the figure. Specifically, thecircuit is a Pierce oscillator which is essentially a Colpittsoscillator having inductance capacitance tank circuit replaced by thequartz crystal. B+ voltage is applied across the cathode and the plateof the triode. The value may be adjusted by varying the potentiometerR-l so as to obtain ap proximately 1.34 volts across R-3. This voltageopposes the mercury cell resulting in zero potential to the recorder.Thus, the recorder measures a signal proportional to the changes in thegrid bias. This grid bias directly reflects changes in amplitude ofvibration of the crystal. The radio frequency choke (RFC) and thecapacity Cl prevent the radio frequency current from entering the directcurrent power supply. Capacity C-2 keeps the radio frequency signal outof the recorder. The crystal is connected directly between the grid andthe plate, and the amount of feedback is dependent on the interelectrodeand stray capacitances between the grid and the cathode and theproperties of the crystal. This feedback and the setting of R-ldetermine the amplitude of vibration of the crystal. The plate tocathode capacitance is shown in the circuit by means of dotted lines.Resistors R-2 and R-3 serve as the grid leak bias. The 10 millivoltrecorder (connected to attenuator A) observes only changes in theamplitude of vibration.

In operation materials capable of being halogenated are detected when afluid containing such materials is contacted with the crystal of thepresent invention employed in such typical circuit. By measuring thechange in frequency of the crystal, change in weight in the substrate ismeasured. This, of course, indicates that halogenation has occurred. inother words, the material susceptible or capable of being halogenatedhas been detected in the fluid material.

EXAMPLE l A detection device of the invention with the bromine complexof polyvinylpyridine was tested with respect to its response fordetecting olefins.

For the purpose of this test a gas containing 300 ppm of propylene innitrogen was passed over the detector at a rate of about cc/min. The gasmixture was heated to a temperature of about F. prior to feeding it intothe analyzer. The analyzer was similar to that shown in the figure. Thedetectors initial stabilized frequency was noted and then the flow oftest gas was begun. Upon contact with the test gas an immediate increasein the frequency was observed indicating that the olefin was halogenatedand the crystal substrate therefore lost weight. The change in frequencywith time is shown in Table I below.

TABLE I Contact Time (Minutes) Change in Frequency (Cycles) Start 2 58 4v 98 6 I17 EXAMPLE 2 The procedure outlined in Example 1 was followedexcept that 100 percent propylene was the test gas. In this environmenta decrease in frequency from the normal frequency of the crystal wasobserved apparently due to absorption by the substrate of the brominatedpropylene. Intermittent purging with nitrogen however resulted in anincrease in the frequency indicating that halogenation had occurred anddemonstrating that the detector could be returned to a stable conditionandbe repeatedly used. The results of this test are outlined in Table IIbelow.

TABLE II Gas Time, Minutes Change in Frequency (Cycles) N, StartPropylene l 16 Propylene l 23 N 5 0 Propylene 2 -84 Propylene 7 l00 6(4-vinyl-pyridine), poly (2-vinylpyridine) and poly(N- vinyl carbazole).

5. The element of claim 1 wherein the charge transfer material is poly(4-vinylpyridine).

6. The element of claim 1 wherein the halogen is se lected from thegroup consisting of bromine, chlorine, iodine, iodine chloride, bromineiodide and bromine chloride.

7. The element of claim 1 wherein the halogen is bromine.

8. In an apparatus for the detection of fluids wherein an electronicoscillation means is controlled by a responsive material in which thesurface of said material is coated with the substrate subjected tocontact with the test fluid, the improvement wherein the substratematerial comprises a halogen complex of a polymeric charge transfermaterial having a nitrogen atom in the repeating unit of the polymer.

9. The improvementof claim 8 wherein the halogen is selected from thegroup consisting of bromine, chlorine, iodine and inter-halogencompounds.

10. The improvement of claim 8 wherein the charge transfer material isselected from the group consisting of poly (2-vinylpyridine), poly(4-vinylpyridine) and poly (N-vinyl carbazole).

11. A method of detecting materials capable of being halogenatedcomprising contacting a test fluid with a coated piezoelectric detector,said detector having a coating of a halogen complex of a polymericcharge transfer material having a nitrogen atom in the repeating unit ofthe polymer, and measuring the change in electrical response of suchcoated piezoelectric crystal detector.

12. The method of claim 11 wherein the test fluid contains an olefin.

13. The method of claim 11 wherein halogen is bromine and the chargetransfer complex is poly (4- vinylpyridine).

2. The element of claim 1 wherein said responsive material is quartz. 3.The element of claim 1 wherein the polymeric charge transfer materialhas an endocyclic nitrogen atom in the repeating unit of the polymer. 4.The element of claim 1 wherein the charge transfer material is selectedfrom the group consisting of poly (4-vinyl-pyridine), poly(2-vinylpyridine) and poly(N-vinyl carbazole).
 5. The element of claim 1wherein the charge transfer material is poly (4-vinylpyridine).
 6. Theelement of claim 1 wherein the halogen is selected from the groupconsisting of bromine, chlorine, iodine, iodine chloride, bromine iodideand bromine chloride.
 7. The element of claim 1 wherein the halogen isbromine.
 8. In an apparatus for the detection of fluids wherein anelectronic oscillation means is controlled by a responsive material inwhich the surface of said material is coated with the substratesubjected to contact with the test fluid, the improvement wherein thesubstrate material comprises a halogen complex of a polymeric chargetransfer material having a nitrogen atom in the repeating unit of thepolymer.
 9. The improvement of claim 8 wherein the halogen is selectedfrom the group consisting of bromine, chlorine, iodine and inter-halogencompounds.
 10. The improvement of claim 8 wherein the charge transfermaterial is selected from the group consisting of poly(2-vinylpyridine), poly (4-vinylpyridine) and poly (N-vinyl carbazole).11. A method of detecting materials capable of being halogenatedcomprising contacting a test fluid with a coated piezoelectric detector,said detector having a coating of a halogen complex of a polymericcharge transfer material having a nitrogen atom in the repeating unit ofthe polymer, and measuring the change in electrical response of suchcoated piezoelectric crystal detector.
 12. The method of claim 11wherein the test fluid contains an olefin.
 13. The method of claim 11wherein halogen is bromine and the charge transfer complex is poly(4-vinylpyridine).